For efficient communication, a receiver should feed back channel information to a transmitter. Generally, a mobile station transmits channel information of a downlink to a base station through an uplink while the base station transmits channel information of the uplink to the mobile station through the downlink. This channel information will be referred to as a channel quality indicator (CQI). The channel quality indicator can be generated by various methods.
FIG. 1 is a diagram illustrating generation and transmission of a channel quality indicator.
The mobile station measures quality of a downlink channel and reports a channel quality indicator value selected based on the measured quality to the base station through a control channel. The base station performs downlink scheduling (selection of mobile station, resource allocation, etc.) in accordance with the reported channel quality indicator.
In other words, when the base station allocates a radio resource to the mobile station in a wireless communication system, the base station uses the channel quality indicator received from the mobile station.
The mobile station measures channel quality information such as signal to interference ratio (SIR) by receiving a pilot channel from the base station and reports the measured channel quality information to the base station. Then, the base station allocates the radio resource to each of the mobile stations using the channel quality information received from each of the mobile stations.
The mobile station can report the channel quality information to the base station periodically or non-periodically. The mobile station can report the channel quality information to the base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH). The physical uplink control channel and the physical uplink shared channel use their respective coding method, and decoding performance of the physical uplink shared channel is more excellent than that of the physical uplink control channel.
In view of time and frequency used by the mobile station to report channel quality information, resources are controlled by the base station, and the channel quality information can be transmitted to the base station periodically or non-periodically. Supposing that the channel quality information periodically reported from the mobile station to the base station is referred to as periodic CQI information and the channel quality information non-periodically reported from the mobile station to the base station is referred to as aperiodic CQI information, physical channels through which the periodic CQI information and the aperiodic CQI information are transmitted in accordance with a scheduling mode in a long term evolution (LTE) system will be expressed by Table 1 below.
TABLE 1PeriodicAperiodic CQICQI informationinformationScheduling modereport channelreport channelFrequency non-selectivePUCCH—Frequency selectivePUCCHPUSCH
Meanwhile, the physical channels through which periodic CQI and aperiodic CQI are transmitted in accordance with the scheduling mode in the LTE system will be described in more detail as follows.
1. The mobile station is requested periodic CQI information from the base station, and configures PUCCH-based periodic CQI information if the PUSCH is not allocated thereto at the timing when the periodic CQI information should be transmitted and transmits the configured periodic CQI information using the PUCCH.
2. The mobile station is requested periodic CQI information from the base station, and configures PUSCH-based aperiodic CQI information if aperiodic CQI information is requested from the base station at the timing when the periodic CQI information should be transmitted and transmits the aperiodic CQI information using the PUSCH. However, data cannot be transmitted to the PUSCH.
3. If aperiodic CQI information is requested from the base station, the mobile station configures PUSCH-based aperiodic CQI information and transmits the CQI information using the PUSCH. However, data cannot be transmitted to the PUSCH.
4. The mobile station is requested periodic CQI information from the base station, and if the mobile station uses the PUSCH to transmit uplink data at the timing when the periodic CQI information should be transmitted, the mobile station configures PUCCH-based periodic CQI information, multiplexes the configured PUCCH-based periodic CQI information with uplink data, and then transmits the multiplexed data using the PUSCH.
To transmit control information more than the amount of information that can be transmitted through the physical uplink control channel or improve transmission performance of the control information, the mobile station transmits the channel quality information to the base station through the physical uplink shared channel. According to the related art, the mobile station can transmit the channel quality information to the base station through the physical uplink shared channel only if there is any grant of the base station.
A 3GPP LTE (3rd generation partnership project long term evolution) system supports a system bandwidth of 1.25 MHz to maximum 20 MHz. Accordingly, a method of transmitting channel quality information according to the related art describes a method of transmitting channel quality information corresponding to a bandwidth of 20 MHz.
However, a long term evolution-advanced (LTE-A) system supports a bandwidth of 100 MHz comprised of five bandwidths of 20 MHz through carrier aggregation. Accordingly, a method of transmitting channel quality information corresponding to a bandwidth of 100 MHz will be required.